Choline acetyltransferase (ChAc) catalyzes the synthesis of the neurotransmitter acetylcholine and is generally considered a specific enzymatic marker for cholinergic neurons. The proposed works for the coming year to study this important enzyme are as follows: 1. To continue our localization of ChAc in rabbit brain, in the basal ganglia of normal human and Huntington's choreic brain by means of the immunohistochemical method. The knowledge from the human study may be of benefit in not only understanding and treating Huntington's disease, but other neurological disorders as well. 2. To develop a specific, sensitive and quantitative radioimmunoassay for ChAc. 3. To elucidate the enzymatic mechanism of ChAc in terms of kinetic studies. 4. To characterize the purified bovine ChAc and possibly mouse ChAc as well, on the molecular level.